1. Field of the Invention
This invention relates generally to methods and apparatus for straightening shafts, and more particularly, to a system for truing large shafts, such as vehicle drive shafts.
2. Description of the Related Art
Vehicle drive shafts are large and tubular, and difficult to manufacture in a manner that they are rendered consistently true. Such shafts, among other shaft products, are very sensitive to bends in their main shaft portions. These imperfections cause noise, vibration, and harshness (“NVH”) issues, and also make final correction balance of the product difficult. One approach to achieving a correction to a vehicle drive shaft is to rotate the vehicle drive shaft while a human operator observes displacements resulting from irregularities. The human operator will apply a force upon the vehicle drive shaft in a direction that tends to compensate for the observed displacements. This not only is a slow process that is difficult to implement in a modern manufacturing environment, it requires significant skill on the part of the human operator. Clearly, the results will vary with the level of skill of the human operator.
The need for increased accuracy in the truing of vehicle drive shafts results in part from the significantly reduced noise emissions from other modern vehicle components, particularly including the drive train. Modern vehicles are sufficiently quiet that drive shaft noise is becoming an increasing portion of overall vehicle operating noise.
To date many tubular products have been manufactured with an excessive amount of run out or bending imperfections. Manufacturers usually attempt to straighten the tubular product using primitive methods such as a static press force applied between two “V” blocks directly on the shaft. The operator approximates how much force or tube deflection is required for straightening the assembly. This is done by rotating the tube between two “V” blocks and monitoring the run out of the assembly on a dial indicator gauge. After establishing the maximum run out the operator will position the tube on its high point, and force the tube into plastic deformation using a ram. The operator will then measure again the amount of bend in the product and repeat the process as many times as needed to reduce the shaft bending into an acceptable tolerance. Bending in this case is defined as the deflection measured between the three points identified by the “V” blocks, and the dial indicator. It should be noted that these points are not the same areas to which the vehicle would react to in actual operation. Many experts in the field of drive shaft manufacturing feel the current straightening operations actually do more harm than good.
It is, therefore, an object of this invention to provide a system whereby a vehicle drive shaft can quickly and simply be trued.
It is another object of this invention to provide a system whereby a vehicle drive shaft can accurately be trued without relying on the skill of a human operator.
The present invention significantly reduces the imperfections in a tubular or cylindrical assembly related to bending. It is therefor well suited to drive shaft manufacturing. Most importantly the invention is also designed to straighten the tubular assembly relative to a rotating datum. The rotating datum is referred to as the True Vehicle Running Center (TVRC) of the product. This process of truing is accomplished at high rates of speed, which suits the operation well to mass production.